The following C code shows different results when build in debug or release mode with Xcode 26.0.1. #include <stdio.h> static void print_fval(int16_t *src) { float fval = (float)((((int32_t)*src) << 16) - (1 << 31)); printf("fval: %f\n", fval); } int main(int argc, const char * argv[]) { int16_t i16[1] = { 0 }; print_fval(i16); return EXIT_SUCCESS; } In debug mode the output is: fval: -2147483648.000000. In release mode the output is: fval: 2147483648.00000. The 1 << 31 might be questionable but I would expect the same outcome in debug or release mode. The difference is in compiling with optimizations or not, compiler option -O0 vs any other optimization option. Would this be considered a compiler/optimizer bug? Older versions of Xcode (15.4 and earlier) do not have this problem.